1. Field
The present disclosure relates to television white space communication systems.
2. Background
Advances in technology have resulted in smaller and more powerful computing devices. For example, there currently exist a variety of portable personal computing devices, including wireless computing devices, such as portable wireless telephones, personal digital assistants (PDAs), and paging devices that are small, lightweight, and easily carried by users. More specifically, portable wireless telephones, such as cellular telephones and Internet Protocol (IP) telephones, can communicate voice and data packets over wireless networks. Many such wireless telephones incorporate additional devices to provide enhanced functionality for end users. For example, a wireless telephone can also include a digital still camera, a digital video camera, a digital recorder, and an audio file player. Also, such wireless telephones can execute software applications, such as a web browser application that can be used to access the Internet. As such, these wireless telephones can include significant computing capabilities.
Electronic devices, such as wireless telephones, may have the ability to communicate via multiple types of wireless networks. One type of wireless network that has been the subject of recent regulatory action is television white space (TVWS). Now that broadcasters have converted analog TV channels to digital, the wireless spectrum formerly occupied by the analog TV channels has become vacant and is available for wireless communication. The Institute of Electrical and Electronics Engineers (IEEE) 802.11af is an amendment (in draft status) to the popular IEEE 802.11 wireless local area network (WLAN) standard, so that Wi-Fi can operate in these vacated frequency regions, which are commonly called television white space.
To communicate via television white space, a device must first scan for available networks (e.g., receive signals from access points operating in the television white space spectrum). Scanning processes may be classified as active or passive. In active scanning, a device transmits a probe message and may receive probe responses from access points. In passive scanning, the device listens for access points without transmitting any data. The Federal Communications Commission (FCC) requires certain TVWS-compatible devices to engage in passive scanning to avoid interference to broadcast TV signals. Typically, this passive scanning process involves listening for television white space access points in all possible/supported television white space channels. The frequency range and bandwidth of television white space channels may differ from one geographic region to another (e.g., North America vs. Europe vs. Japan). Moreover, even within the same geographic region, a particular television white space channel may be available in one area but not another due to the existence of a television station that broadcasts on the channel in one area but not the other. Thus, the process of scanning all possible television white space channels may be time consuming. For example, if access points transmit detectable messages every 100 ms, then scanning a few hundred possible television white space channels (i.e., frequency/bandwidth combinations) may take a few minutes.
In some television white space networks, an access point may provide a device with a white space map (WSM). The WSM may identify which television white space channels are available to the device and which television white space channels are not available to the device. However, until a WSM is received, the device may perform a brute-force search of all possible television white space channels, which may be time consuming and may expend battery resources at the device.